Abstract A direct and regioselective route to symmetrical [4]-dendralenes has been developed based on nickel-catalyzed electroreductive homocoupling of α-allenyl electrophiles. The methodology offers the first electrochemical approach to dendralenes and a rare example of nickel-mediated activation of α-allenyl electrophiles. Under mild conditions in an undivided cell, a broad range of α-, β-, and δ-substituted allenyl acetates undergo efficient dimerization to furnish diversely substituted cross-conjugated tetraenes in moderate to good yields. Aryl-substituted substrates display particularly high stereocontrol, generally affording the corresponding dendralenes with excellent preference for the (E,E)-diastereomer. This work introduces a complementary reductive disconnection for [4]-dendralene synthesis and reveals a previously unexplored dimerization manifold of α-allenyl electrophiles.
Abstract The ability of telluronium [Ar3Te]+ to bind crown ethers and acyclic polyethers through chalcogen bonding is investigated in the solid state and in solution. X-ray diffraction of several 1:1 complexes revealed short Te···O interactions (dTe–O below the sum of van der Waals radii) and high linearity (Ar–Te–O angles in the range 163–178°). NMR and DOSY (diffusion-ordered NMR spectroscopy) experiments confirm that these interactions persist in solution. Isothermal titration calorimetry provides the thermodynamic parameters for the telluronium–crown ether and telluronium–polyether equilibria, with association constants reaching Ka ∼ 106 M–1 for the 5- to 7-membered crown ethers. Based on these results, selective coordination of certain crown ethers was efficiently achieved. Furthermore, the templating effect of the telluronium on acyclic polyethers is further demonstrated by its ability to promote the ring closure of a long polyether bearing both bromo and hydroxy termini. Theoretical analysis of the ligand-Te interaction points to a dominant Coulombic contribution, supported by dispersion forces, in stabilizing polyether binding to the Te center. Although the minor covalent contribution operates a crucial anchoring role, it is not sufficient to restrict the O atoms to exclusive σ-hole interactions, suggesting a fluxional dynamic behavior in solution in which all O atoms dynamically interact with the Te center.
Abstract Electrochemical CO2 capture and concentration (eCCC) systems have the potential to operate at efficiencies higher than those of thermal systems. Quinones have been the focus of many eCCC studies as redox carriers, as they can capture or release CO2 depending on their oxidation states. Quinones (Q) with higher cathodic potentials bind CO2 more strongly when they are reduced; however, higher cathodic potentials result in O2 sensitivity. Intra- and intermolecular noncovalent interactions have been explored to anodically shift the second reduction potential (E1/2(Q–1/Q–2)) while maintaining the CO2 binding affinity (log(KCO2)). In this report, we investigate the effects of four trialkyl borate additives, B(OMe)3, B(OEt)3, B(OiPr)3, and B(OBu)3, on the second reduction potential (E1/2(Q–1/Q–2)) and CO2 binding affinity (log(KCO2)) of three quinones, 2-chloro-1,4-benzoquinone (2-ClBQ), 2,3,5,6-tetrafluoro-1,4-benzoquinone (TFQ), and 2,3,5,6-tetrachloro-1,4-benzoquinone (TCQ). Changes in the second reduction potential ranged from 0 to 430 mV with up to 300 equiv of these additives. The magnitude of the anodic shift of the quinones is correlated to the Lewis acidity of the trialkyl borate additive and the Lewis basicity of the quinone. We then investigated the effect of trialkyl borate additives on log(KCO2), which decreases for TFQ and 2-ClBQ but remains constant for TCQ. These results underscore the importance of understanding the additive and quinone interactions in eCCC systems.
Abstract Quinoline-based chromophores are of great interest in medicinal chemistry due to their ability to bind DNA, modulate key biochemical pathways, and serve as fluorescent probes for molecular recognition and therapeutic applications. The incorporation of chalcogen atoms further broadens the functional scope of these systems; S and Se can modulate electronic distribution, polarizability, and photophysical behavior through chalcogen bonding and heavy-atom effects. Building on these properties, we rationally designed and synthesized 11 quinoline- and organochalcogen-based derivatives, achieving yields of 10–75% through a simple and efficient method involving the introduction of various electron-donating and electron-withdrawing substituents, as well as different chalcogen atoms (Se and S), including one Se derivative in a higher oxidation state. These compounds were subjected to systematic photophysical, electrochemical, reactive oxygen species generation, and DNA-binding studies. The fluorescence analyses revealed intense UV absorption and low to moderate fluorescence quantum yields, both of which were by the nature of the chalcogen atom. Selenium derivatives displayed reduced emission and were more susceptible to oxidation, whereas selenoxide exhibited a larger electrochemical band gap. The data indicated a preference for minor groove DNA binding, with the π-extended derivative showing the highest affinity. This integrated approach highlights the potential of quinoline-organochalcogen hybrids as multifunctional platforms for advanced applications in photophysics, electrochemistry, and DNA-targeted therapeutics.
Abstract Electrochemical control over Brønsted acidity offers a powerful strategy for regulating proton-transfer reactivity, yet organic redox-switchable acids remain rare. Here we report a julolidine–benzothiadiazole-functionalized phenol that combines a donor–acceptor π system with an acidic O–H bond in a single molecular scaffold. The phenol exhibits a pKa of 23.6 in acetonitrile and undergoes reversible oxidation in both its protonated and deprotonated forms. Single-electron oxidation lowers the O–H pKa to 13.5. Electrochemical studies further suggest that single-electron reduction suppresses the O–H bond acidity, leading to a pKa of 27.7 and an overall electrochemically accessible acidity window of approximately 14 pKa units. Density functional theory indicates that oxidation and reduction are governed by electronically complementary julolidine donor and benzothiadiazole acceptor fragments, respectively. This provides a molecular basis for the ambipolar electrochemical behavior. Our results demonstrate that ambipolar donor–acceptor molecular design provides a strategy for achieving bidirectional electrochemical modulation of Brønsted acidity.
